Int. J. Electrochem. Sci., 14 (2019) 6814 – 6825, doi: 10.20964/2019.07.75 International Journal of ELECTROCHEMICAL SCIENCE www.electrochemsci.org Electrochemical Studies of Bitter Gourd (Momordica charantia) fruits as Ecofriendly Corrosion Inhibitor for Mild Steel in 1 M HCl Solution Aijuan Zhao1, Haijie Sun1,*, Lingxia Chen1, Yufang Huang1, Xingjie Lu2,*, Bing Mu1, Hairong Gao1, Shaoqing Wang1, Ambrish Singh3 1 Institute of Environmental and Catalytic Engineering, College of Chemistry and Chemical Engineering, Zhengzhou Normal University, Zhengzhou 450044, Henan, China. 2 Henan Institute of Metrology, Zhengzhou-450000, Henan, China. 3 School of Materials Science and Engineering, Southwest Petroleum University, Chengdu, Sichuan 610500, China. *E-mail: [email protected], [email protected] Received: 9 March 2019 / Accepted: 22 April 2019 / Published: 10 June 2019 Fruits extract of Momordica charantia (MCFE) was characterized using gas chromatography (GC), and mass spectrometry (MS) methods. The influence of MCFE on corrosion of mild steel in 1M HCl solution was evaluated using static electrochemical methods. Electrochemical Impedance Spectroscopy (EIS) and polarization studies were performed to derive the kinetic mechanism taking place at the electrodes. Micro-electrochemical tests were performed using scanning electrochemical microscopy (SECM) technique. The surface was further examined by scanning electron microscope (SEM). The EIS results suggested that the increase in the concentration of MCFE increased the inhibition efficiency. Polarization statistics pointed towards the changes in the anodic and cathodic kinetics, but overall shift of –Ecorr was less than 85 mV suggesting the MCFE inhibitor belongs to mixed type category. SEM studies revealed that the surface of the mild steel was quite unaffected with MCFE film on it in 1M HCl solution. Keywords: Mild steel; Momordica charantia; Corrosion; EIS; SECM; GC-MS 1. INTRODUCTION Presence of scales, intermetallics, precipitates and debris inside the pipelines is a major blow to the oil companies as it reduces the production as well as the transportation. Acids in different volume are used to dissolve and clean these unwanted substances stuck to the pipelines. In the process of cleaning the pipes the acids do attack the pipelines and corrodes the metal surface. This can cause fatal injuries, accidents due to leakage and failure of the overall systems. Corrosion is a global problem and a lot of Int. J. Electrochem. Sci., Vol. 14, 2019 6815 money is being used to mitigate it. Almost all countries use 0.1-3% of their GDP in solving problems or finding replacements caused due to corrosion. Apart from the corrosive nature of the acids, pH and temperature also play a vibrant part in the evaluation of corrosion rate. Although, the mechanism of the formation and removal of the precipitates, intermetallics, debris and scaling is not entirely assumed due to the complicated reaction processes [1]. The literatures and available techniques suggests that still there is no method to control corrosion or to stop it completely. The process can be delayed with the use of several methods including, cathodic protection, galvanization, coating/spraying, and inhibitors. Inhibitors are chemical substances that are added to the system to mitigate corrosion. These substances adsorb on to the surface of the metal forming a film that keeps the corrosive media away from the metal. The use of inhibitors is one of the greatest technique used worldwide due to its low price, ease of usage, no requirement of special equipment’s and availability [2-5]. Most of the inhibitors used are organic and their usage in higher concentrations are strictly forbidden by the environmental regulating authorities. As the higher concentration can affect the toxicity level and cause various problems. So, to keep these regulations and environment in front, use of ecofriendly inhibitors are in high demand. They are environment friendly, non-toxic and biodegradable that can be use in higher concentrations too. Many alkaloids, steroids, amines, fatty acids etc. are derived from plants which serve as an effective inhibitor. The heteroatoms (N, S, O), benzene ring, -bonds presence in the inhibitors decide the potential and effectiveness of an inhibitor [6-10]. The inhibitor Momordica charantia used for the present study was selected for its recognized bitterness s shown in figure 1. It is also well-known as bitter melon, Okinawa, karavella (karela), balsam pear, bitter gourd or bitter squash. It is classified in the clan of Cucurbitaceae, and is broadly found in Asia, Africa, and the Caribbean for its edible fruit. Originally from India and was introduced to China later in the 14th century and now egg mixed with bitter gourd is a famous dish with the bitter melon tea in the mainland. The bitterness of the plant is due to the chemical substance Momordicin present in the fruit. The plant is rich in momordicin I, momordicin II, terpenoid compounds (including momordicin- 28, momordicinin, momordicilin, momordenol, momordol), glycosides (including momordin, charantin, charantosides, goyaglycosides, momordicosides) and cucurbitacin B [11]. The regular use of the fruit can increase the beta cells in the pancreas which can further increase the insulin level thereby controlling Diabetes [12-16]. In contemporary research work we have investigated MCFE as corrosion mitigator of mild steel in HCl media through weight loss, electrochemical and surface studies. Figure 1. Momordica charantia found in (a) India and (b) China. Int. J. Electrochem. Sci., Vol. 14, 2019 6816 2. EXPERIMENTAL 2.1. Grounding of inhibitor The fruits of Momordica charantia were purchased from the vegetable market and were dehydrated in sun. 100 grams of desiccated Momordica charantia fruits were soaked in 900 ml of ethanol for 24 hours and refluxed for 5 hours. The extract was then mixed with reagent grade HCl and accumulated to 500 ml. The solution was further diluted to 25, 50, 100, 200 v/v (equivalent to 2%, 5%, 10% and 20% v/v wt. %) with HCl to prepare the four different concentrations of the inhibitor. The hostile solution of HCl (corrosion medium) was prepared by pure hydrochloric acid with double distilled water. The reagent grade HCl bottle was purchased from the chemical supplier in china. This solution was availed to elucidate the corrosion mitigation parameters. 2.2. Preparation of materials Mild steel samples were mechanically abraded conferring to ASTM A262 standard and used for the corrosion study. The samples were washed repeatedly with H2O and alcohol to remove any kind of adulteration and then dried at room temperature. The samples were covered with epoxy resin and left overnight to dry. As 1 cm2 surface is required for the electrochemical studies. The samples were welded with copper wire and then placed in round utensil. This round utensil was filled with epoxy resin and left to dry overnight. Next day the sample with epoxy resin was (now round in shape due to round utensil) taken out and the bottom part was abraded continuously with different grades of emery paper (200, 400, 600, 800 and 1200). Once the bottom part of the mild steel (1 cm2) was seen clearly, it was then polished mechanically for a mirror finish. 2.3. Gas Chromatography (GC) GC-2010 Plus machine by Shimadzu Japan was used to perform the gas chromatography tests. GC device was prepared with a single injector and two flame ionization detectors (FID). He (1 mL/min) was used as the carrier gas used in the process. Relative component concentrations were analyzed based on GC peak areas without using correction factors. Figure 2. Gas chromatography peaks obtained for MCFE extract using flame ionization detector. Int. J. Electrochem. Sci., Vol. 14, 2019 6817 A number of noticeable peaks as shown in figure 2 were identified in the repeated GC investigations of the extract. Most of the peaks (1.388~1.674) are of terpenoids and similar to the already published work [17]. Among the peaks identified, they are very similar to Momordicin and other terpenoids [18]. 2.4. Mass Spectrometry (MS) GC7890-MS5975 (Agilent, USA) machine was used to perform the mass spectroscopy prepared with a HP-5MS capillary column (30 mm × 0.32 mm × 0.25 μm) and quadruple mass spectrometer. He (1 mL/min) was used as the carrier gas used in the process. Among the peaks identified, they are very similar to Momordicin, terpenoids and glycosides as shown in figure 3. The peaks obtained at 44.1, 66, 89, 119, correspond to the momordicin-28, momordicinin, momordicilin, momordenol terpenoids present in the fruit extract. Glycosides are lower in concentration so their peaks are at very intensity. All the peaks (Fig. 2) were matched in NIST library with their individual CAS number to get the exact information about the peaks [19]. Int. J. Electrochem. Sci., Vol. 14, 2019 6818 Figure 3. Mass spectrometry peaks of various components present in MCFE extract. 2.5. Electrochemical measurements Three cell assembly of counter electrode, reference electrode and working electrode was employed to carry out the electrochemical tests on Autolab workstation. Nova and Zsimpwin softwares were used to analyze the obtained data. The tests were started after an immersion time of 30 minutes to ensure a stable potential. To attain this, an open circuit potential (OCP) test was performed for ~30 minutes vs. SCE to ensure the stable potential. The frequency ranges of 100 kHz to 10 mHz was selected to carry out all the electrochemical impedance spectroscopy (EIS) tests. The polarization tests were conducted at the potential of -250 mV to +250 mV with scan rate of 1 mV/s [20, 21]. Scanning electrochemical microscopy (SECM) was used to detect the localized changes on the metal surface using CHI900C workstation. The three cell electrode assembly was employed for the test but the size was much smaller than that used in the traditional electrochemical tests. The room temperature was maintained using the thermostat for all the experiments in absence and presence of inhibitors.